Electric working machine and method of detecting fault in electric working machine

ABSTRACT

An electric working machine in one aspect of the present disclosure includes a motor, a drive current path, a resistor, a first current detector, a second current detector, and a fault determiner. The drive current path supplies the drive current to the motor. The resistor is disposed on the drive current path so as to receive the drive current. The first current detector detects a first detection value based on a first electromagnetic phenomenon with respect to the resistor. The second current detector detects a second detection value based on a second electromagnetic phenomenon with respect to the resistor. The fault determiner performs a faulty state determination based on the first detection value and the second detection value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2019-186285 filed on Oct. 9, 2019 with the Japan Patent Office, the entire disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to an electric working machine. Japanese Unexamined Patent Application Publication No. 2019-123027 discloses an electric working machine configured to detect a drive current based on a voltage across a resistor disposed on a drive current path.

SUMMARY

If the electric working machine mentioned above is kept in a faulty state in which the drive current cannot be appropriately detected, the electric working machine cannot control itself properly. This may cause a failure in the electric working machine.

In one aspect of the present disclosure, it is desirable to avoid continuing an inappropriate detection of a drive current in an electric working machine.

An electric working machine in one aspect of the present disclosure includes a motor, a drive current path, a resistor, a first current detector, a second current detector, and/or a fault determiner.

The drive current path supplies the drive current to the motor. The drive current is supplied to the motor to drive the motor. The resistor is disposed on the drive current path so as to receive the drive current.

The first current detector detects a first detection value based on a first electromagnetic phenomenon with respect to the resistor. The first detection value indicates a magnitude of the drive current. The first electromagnetic phenomenon varies in accordance with a flow of the drive current through the resistor. The second current detector detects a second detection value based on a second electromagnetic phenomenon with respect to the resistor. The second detection value indicates the magnitude of the drive current. The second electromagnetic phenomenon varies in accordance with the flow of the drive current through the resistor. The second electromagnetic phenomenon is different (or distinct) from the first electromagnetic phenomenon.

The fault determiner performs a faulty state determination based on the first detection value and the second detection value. The fault determiner determines whether the first current detector or the second current detector is in a faulty state during the faulty state determination.

As mentioned above, the second electromagnetic phenomenon varies in accordance with the drive current flowing through the resistor. Thus, if both the first current detector and the second current detector are in a non-faulty state, the first detection value and the second detection value are equal or substantially equal to each other. On the other hand, if the first current detector and/or the second current detector is/are faulty, the first detection value and the second detection value may be different (or distinct) from each other.

The electric working machine thus enables a determination of a fault in the first current detector or the second current detector by the faulty state determination.

Accordingly, the electric working machine as described above avoids continuing to inappropriately detect the drive current due to the fault in the first current detector or the second current detector. This enables the electric working machine to avoid driving the motor by the drive current having an inappropriate magnitude, thereby reducing a failure in the electric working machine. Alternatively, the second electromagnetic phenomenon may be same as the first electromagnetic phenomenon. In the electric working machine with such configuration, if the first current detector and/or the second current detector is/are faulty, the first detection value and the second detection value may be different (or distinct) from each other.

The first electromagnetic phenomenon and the second electromagnetic phenomenon may correspond to any electromagnetic phenomenon. The first electromagnetic phenomenon may correspond to a voltage across the resistor. The second electromagnetic phenomenon may correspond to a magnetic field across the resistor.

That is, when the drive current flows through the resistor, the voltage is generated across the resistor, and further the magnetic field is generated around the resistor. This enables the first current detector and the second current detector to detect the magnitude of the drive current based on the different (or distinct) electromagnetic phenomenons caused by the drive current.

Thus, the electric working machine enables a determination of a fault in the first current detector or the second current detector, avoiding continuously detecting the drive current by the first current detector in the faulty state or the second current detector in the faulty state.

The electric working machine as described above may include a switch and/or a first interruption controller. The switch may be disposed on the drive current path. The switch may be configured to switch between an established state and an interruption state. The switch in the established state may establish the drive current path. The switch in the interruption state may interrupt the drive current path. The first interruption controller may place the switch in the interruption state in response to an establishment of a first determination condition. The first determination condition may be established in response to the fault determiner determining that the first current detector or the second current detector is in the faulty state.

The electric working machine enables supply of the drive current to the motor to be forcibly stopped by the switch and the first interruption controller when the first current detector or the second current detector is in the faulty state. Accordingly, the electric working machine avoids a runaway of the motor caused by the faulty state of the first current detector or the second current detector, enabling reduction in damages of the motor and the electric working machine.

The electric working machine described above may further include a second interruption controller provided independently from the first interruption controller. The second interruption controller may place the switch in the interruption state in accordance with an error being greater than a determination criteria. The error may correspond to a difference between the first detection value and the second detection value. The determination criteria may correspond to a threshold to place the switch in the interruption state.

In the electric working machine, in a case in which the first interruption controller is unable to place the switch in the interruption state due to some cause, the second interruption controller places the switch in the interruption state. This enables the drive current path to be interrupted. Accordingly, in a case in which the first current detector or the second current detector is in the faulty state, the electric working machine enables the supply of the drive current to the motor to be forcibly stopped.

The first current detector may output a first detection signal. The first detection signal may vary in accordance with the first detection value. The second current detector may output a second detection signal. The second detection signal may vary in accordance with the second detection value. The electric working machine may include a first operational amplifier and/or a second operational amplifier. The first operational amplifier may have a first slew rate. The first operational amplifier may amplify the first detection signal. The second operational amplifier may have a second slew rate. The second operational amplifier may amplify the second detection signal. The first slew rate may be equal or substantially equal to the second slew rate.

As described above, in a case in which the first slew rate and the second slew rate are equal or substantially equal to each other, it is less likely to cause a delay in change between the first detection signal amplified by the first operational amplifier and the second detection signal amplified by the second operational amplifier. As a result, the electric working machine enables reduction in occurrence of a detection error caused by a delay in change between the first detection signal and the second detection signal when the first detection current and the second detection current are compared with each other.

Here, “the first slew rate and the second slew rate are equal or substantially equal to each other” may mean that not only the first slew rate and the second slew rate are exactly the same, but also the first slew rate and the second slew rate have a difference between the first slew rate and the second slew rate within a permissible range.

The electric working machine described above may further include a detector, a circuit board, and/or a detection path. The detector may include the resistor, the second current detector, a first connection terminal, and/or a second connection terminal. The resistor may have a first end and a second end. The first connection terminal may be electrically connected to the first end. The second connection terminal may be electrically connected to the second end. The circuit board may include the drive current path, the first current detector, and the detector thereon. The detection path may be disposed on the circuit board. The detection path may electrically connect the resistor to the first current detector.

The drive current path may be electrically connected to the resistor via the first connection terminal and the second connection terminal. The circuit board may include a first area where the detector is disposed. The drive current path may include a first partial path disposed out of (or deviating from) the first area on the circuit board. The drive current path may be connected to the first connection terminal and the second connection terminal in the first area. The detection path may include a detection end and an inclusion region. The detection end may be connected to the first connection terminal and the second connection terminal. The inclusion region may be adjacent to the detection end. The inclusion region may be included in the first area.

The inclusion region is separated from the first partial path. This enables reduction in an electromagnetic interference of the detection path (in particular, the inclusion region) with the drive current path (in particular, the first partial path) in a surrounding of the first connection terminal and the second connection terminal.

The first region is not limited to a two-dimensional region, but may be a three-dimensional region. The circuit board may include a first surface and a second surface opposing the first surface. The detector may be disposed on the first surface. The three-dimensional region may extend from the first surface to the second surface.

The circuit board may include two or more current paths in the first area. The two or more current paths may flow a circuit board current (i.e. an electric current through the circuit board). The circuit board current may include a current component parallel to the flow of the drive current through the resistor. The current component in the first area may have a magnitude equal to or less than 20 mA.

The current component generates a magnetic field, enabling reduction in an influence of the magnetic field on the second current detector. Accordingly, this enables reduction in a detection error in the magnitude of the drive current based on the second electromagnetic phenomenon.

The electric working machine described above may include a current fluctuation determiner. The current fluctuation determiner may determine whether a fluctuation value is greater than a fluctuation determination value. The fluctuation value may correspond to a first error during a determination period or a second error during the determination period. The determination period may be specified in advance to determine the fluctuation value. The first error may be a difference between a maximum value of the first detection value and a minimum value of the first detection value. The second error may be a difference between a maximum value of the second detection value and a minimum value of the second detection value. The fluctuation determination value may correspond to the fluctuation value when the first current detector or the second current detector is in the faulty state.

The fault determiner may perform the faulty state determination based on the first detection value and the second detection value during the determination period, in response to the fluctuation determiner determining that the fluctuation value is equal to or less than the fluctuation determination value. The fault determiner may avoid performing the faulty state determination, in response to the current fluctuation determiner determining that the fluctuation value is greater than the fluctuation determination value.

In the electric working machine, it depends on a determination made by the current fluctuation determiner whether to perform faulty sate determination. During the determination period in which the fluctuation value is determined to be greater than the fluctuation determination value, the drive current is widely fluctuated, and thereby may cause an erroneous determination in the faulty state determination. Thus, the electric working machine does not perform the faulty state determination by the fault determiner during such determination period, thereby enabling reduction in the erroneous determination in the faulty state determination.

The fault determiner may repeatedly acquire the first detection value to thereby acquire a first series of detection values. The fault determiner may calculate a first mean value. The first mean value may indicate a mean of the first series of detection values. The fault determiner may repeatedly acquire the second detection value to thereby acquire a second series of detection values. The fault determiner may calculate a second mean value. The second mean value may indicate a mean of the second series of detection values. The fault determiner may perform the faulty state determination based on the first mean value and the second mean value.

As described above, use of the first mean value and the second mean value enables reduction in an influence of a momentary noise included in the first detection value and the second detection value, while allowing for the faulty state determination. This enables the electric working machine to reduce the influence of the momentary noise while performing the faulty state determination, thereby avoiding a decrease in determination accuracy of the fault determination.

The first mean value may indicate a mean of the first series of detection values in a continuous time series. The second mean value may indicate a mean of the second series of detection values in a continuous time series. The first mean value may indicate a mean of the first series of detection values in a discrete time series. The second mean value may indicate a mean of the second series of detection values in a discrete time series.

The electric working machine described above may further include a battery pack configured to output the drive current. The electric working machine can apply the drive current to the motor from the battery pack.

The electric working machine described above may further include a trigger switch configured to be pulled (or squeezed) by a user of the electric working machine. The trigger switch may be turned on in response to the user pulling the trigger switch. The fault determiner may determine that the first current detector and the second current detector are in a non-faulty state, in response to (i) the first current detector or the second current detector being in the faulty state, and (ii) the trigger switch being turned off.

In the electric working machine, after the first current detector or the second current detector is determined to be in the faulty state, a release of a result of the determination performed by the fault determiner can be achieved by the user turning off the trigger switch. Here, “a release of a result of the determination” means a determination that the first current detector and the second current detector are in a non-faulty state. Thus, after the first current detector or the second current detector is determined to be in the faulty state, the user enables an operation to release the faulty state.

The resistor may be disposed on the drive current path so as to detect the magnitude of the drive current.

The present disclosure in another aspect discloses a method of detecting a fault in an electric working machine, the method including:

detecting a first detection value by a first current detector of the electric working machine based on a first electromagnetic phenomenon with respect to a resistor of the electric working machine, the drive current being supplied to a motor of the electric working machine to drive the motor, the resistor being disposed in the electric working machine so as to receive the drive current, and the first electromagnetic phenomenon varying depending on a flow of the drive current through the resistor;

detecting a second detection value by a second current detector of the electric working machine based on a second electromagnetic phenomenon with respect to the resistor, the second electromagnetic phenomenon being different (or distinct) from the first electromagnetic phenomenon, the second electromagnetic phenomenon varying depending on the flow of the drive current through the resistor; and/or

detecting occurrence of a fault in the first current detector or the second current detector based on the first detection value and the second detection value.

This method exerts functions similar to the above-described electric working machine.

BRIEF DESCRIPTION OF THE DRAWINGS

An example embodiment of the present disclosure will be described hereinafter by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view showing an overall configuration of an electric working machine of a first embodiment;

FIG. 2 is a block diagram showing an electrical configuration of the electric working machine;

FIG. 3 is an enlarged perspective view of a neighboring area of a detector arrangement region;

FIG. 4 is an explanatory diagram schematically showing current through two or more current paths arranged in the detector arrangement region;

FIG. 5 is a flowchart showing a working machine control processing;

FIG. 6 is a flowchart showing a current measurement processing;

FIG. 7 is a flowchart showing a failure diagnosis processing; and

FIG. 8 is an explanatory diagram showing a time period for executing comparison of a drive current based on a current waveform.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure is not limited to embodiments below, and may be carried out in various forms within the technical scope of the present disclosure.

1. First Embodiment

[1-1. Overall Configuration]

As shown in FIG. 1, an electric working machine 1 of the present embodiment is embodied as a circular saw.

The electric working machine 1 includes a base 2 and a main body 3. The base 2 has a substantially rectangular member that is brought into contact with an upper surface of a workpiece. The main body 3 is arranged on an upper surface side of the base 2. When the electric working machine 1 performs cutting operation of the workpiece, the base 2 is used in contact with the workpiece to be cut.

The main body 3 includes a circular saw blade 4, a saw blade case 5, and a cover 6. The saw blade 4 is arranged on a right side of the main body 3 in a forward cutting direction. The saw blade case 5 houses a peripheral edge of substantially an upper semicircular area of the saw blade 4.

The cover 6 covers a peripheral edge of substantially a lower semicircular area of the saw blade 4. The cover 6 is openable and closable, and FIG. 1 shows a state where the cover 6 is closed. The electric working machine 1 is moved in the forward cutting direction during cutting of the workpiece, thereby causing the saw blade 4 to rotate in a clock wise direction in FIG. 1, and thus the cover 6 is gradually opened. Accordingly, the saw blade 4 is exposed, and its exposed part is made to cut into the workpiece.

The main body 3 is provided with a motor case 7 on a left side of the main body 3. The motor case 7 is substantially cylindrical. The motor case 7 houses a motor 11 that serves as a drive source of the electric working machine 1. The motor 11 is shown not in FIG. 1, but in FIG. 2.

A gear mechanism (not shown) is housed between the motor case 7 and the saw blade 4. Rotation of the motor 11 is transmitted to the saw blade 4 via the gear mechanism, causing the saw blade 4 to rotate.

A handle 8 to be gripped by a user of the electric working machine 1 is arranged on an upper side of the main body 3. The handle 8 is mounted in an arch shape on the upper side of the main body 3. The handle 8 includes a first fixing end 8 a and a second fixing end 8 b. The first fixing end 8 a is fixed to a rear end of the main body 3 along the forward cutting direction. The second fixing end 8 b is fixed to a forward part of the main body 3 along the forward cutting direction relative to the first fixing end 8 a.

The handle 8 includes a trigger switch 9. The trigger switch 9 is configured to be pulled (or squeezed) by the user. The user can pull or release the trigger switch 9 while gripping the handle 8. The user can pull the trigger switch 9 with operating a lock-off lever. Specifically, the user can pull the trigger switch 9 by pressing the lock-off lever from a left or right side. The lock-off lever protrudes in a left-right direction of the handle 8 near the trigger switch 9. The trigger switch 9 is pulled to turn on the electric working machine 1, and the trigger switch 9 is released to turn off the electric working machine 1.

At the rear end of the main body 3, a battery pack 10 is detachably attached. The battery pack 10 includes a battery 12 (shown in FIG. 2) that is rechargeable. When the trigger switch 9 is pulled with the battery pack 10 being attached to the main body 3, the motor 11 is rotated by electric power from the battery 12.

[1-2. Electrical Configuration]

An electrical configuration of the electric working machine 1 will be described below.

As shown in FIG. 2, the electric working machine 1 includes a controller 20. The controller 20 includes a power supply terminal 20 a and a ground terminal 20 b. When the battery pack 10 is attached to the main body 3, the power supply terminal 20 a and the ground terminal 20 b are connected to a power supply terminal 10 a and a ground terminal 10 b of the battery pack 10, respectively. The ground terminal 20 b is electrically connected to a ground 49. The ground 49 has a reference voltage.

The battery 12 includes a positive electrode connected to the power supply terminal 10 a. The battery 12 also includes a negative electrode connected to the ground terminal 10 b.

The controller 20 and the battery pack 10 may include communication terminals. The controller 20 and the battery pack 10 may transmit and receive various signals via the communication terminals. The battery pack 10 may output a discharge permission signal or a discharge prohibition signal to the controller 20. The discharge permission signal notifies that the battery pack 10 is in a dischargeable state, and the discharge prohibition signal notifies that the battery pack 10 is in a non-dischargeable state.

The controller 20 receives electric power from the battery 12 of the battery pack 10 to drive and control the motor 11. In the present embodiment, the motor 11 is a three-phase brushless motor (BLM).

The controller 20 includes a motor driver 21, a control circuit 23, a regulator 24, a motor current path 25 (or a drive current path 25), a detection path 27, a breaker switch 41, a detector 43, an auxiliary interruption controller 45, and a first current detector 47.

The motor driver 21 is a circuit that receives the electric power from the battery 12 and that supplies a drive current Idr into three phase windings of the motor 11. The drive current Idr drives the motor 11. In the present embodiment, the motor driver 21 is in a form of a three-phase full-bridge circuit including six switching devices (not shown). In the present embodiment, the six switching devices may be each a Metal oxide semiconductor field effect transistor (MOSFET), but are not limited to the MOSFET.

The motor driver 21 is electrically connected to terminals U, V, and W of the motor 11, and to the motor current path 25. The motor current path 25 is configured to supply the drive current Idr from the battery pack 10 to the motor 11. The motor current path 25 includes a power-supply line 25 a and a ground line 25 b.

The motor driver 21 is connected to the power-supply line 25 a and the ground line 25 b. The power-supply line 25 a connects the power supply terminal 20 a with the motor driver 21. The breaker switch 41 is disposed on the power-supply line 25 a. The ground line 25 b connects the motor driver 21 with the ground terminal 20 b. The detector 43 is disposed on the ground line 25 b.

The motor driver 21 turns on or off the above-described switching devices in accordance with control signals Smd. The control signals Smd are output from the control circuit 23. The motor driver 21 turns on or off the individual switching devices, thereby supplying currents into respective phase windings of the motor 11 to rotate the motor 11.

The control circuit 23 in the present embodiment is a microcomputer including a CPU 23 a, a ROM 23 b, and a RAM 23 c; however, the control circuit 23 is not limited to the microcomputer. Various functions of the control circuit 23 are achieved when the CPU 23 a executes a program stored in a non-transitory tangible storage medium. In this example, the ROM 23 b corresponds to the non-transitory tangible storage medium storing the program. When the CPU 23 a executes the program, a method corresponding to the program is performed. The various functions to be performed by the CPU 23 a may be partially or entirely achieved by one or more integral circuits, or one or more discrete devices. The control circuit 23 may include two or more microcomputers.

The control circuit 23 is configured to control the drive current Idr by controlling the motor driver 21.

The regulator 24 receives the electric power from the battery 12 via the power supply terminal 20 a to generate a circuit voltage Vcc of (e.x. 5V) for operating the control circuit 23.

The breaker switch 41 switches between an established state or an interruption state in accordance with a command signal St1 from the control circuit 23 and a command signal St2 (hereinafter, also referred to as a fault detection signal St2) from the auxiliary interruption controller 45. The breaker switch 41 may include a MOSFET, or a switching device in other forms. The breaker switch 41 in the established state establishes the drive current path 25. The breaker switch 41 in the interruption state interrupts the drive current path 25.

The detector 43 includes a resistor 43 a, a second current detector 43 b, a second operational amplifier 43 c, a first connection terminal 43 d, and a second connection terminal 43 e.

The resistor 43 a is disposed on the drive current path 25 so as to receive the drive current Idr. The resistor 43 a is electrically connected to the drive current path 25 via the first connection terminal 43 d and the second connection terminal 43 e. The resistor 43 a has a first end 43 a 1 and a second end 43 a 2. The first connection terminal 43 d is electrically connected to the first end 43 a 1. The second connection terminal 43 e is electrically connected to the second end 43 a 2.

The second current detector 43 b is arranged adjacently to the resistor 43 a. The second current detector 43 b includes a Hall element to detect a magnetic field generated around the resistor 43 a. The second current detector 43 b detects the magnetic field by conducting current to the resistor 43 a. The second current detector 43 b outputs a second detection signal Smc. The second detection signal Smc varies in accordance with the detected magnetic field (in particular, a magnetic flux density passing through the second current detector 43 b). In other words, the second current detector 43 b is configured to detect current (in particular, the drive current Idr) through the drive current path 25 based on the magnetic field around the resistor 43 a. The second detection signal Smc is a detection signal indicative of the drive current Idr detected by the second current detector 43 b. The drive current Idr is also referred to as a second detection current Idr2 below. The magnetic field generated around the resistor 43 corresponds to one example of the second electromagnetic phenomenon of the present disclosure. The magnitude of the drive current Idr (or the second detection current Idr2) corresponds to one example of the second detection value of the present disclosure.

The second operational amplifier 43 c has a second slew rate. The second operational amplifier 43 c includes an inputter and an outputter. The inputter is connected to the second current detector 43 b, and the outputter is connected to the control circuit 23. The outputter of the second operational amplifier 43 c is connected not only to the control circuit 23, but also to the auxiliary interruption controller 45. When the second detection signal Sine is input to the inputter, the second operational amplifier 43 c amplifies the second detection signal Smc, and then outputs the amplified second detection signal Smc from the outputter.

The first current detector 47 includes a first operational amplifier 47 a, a first inputter 47 b, a second inputter 47 c, and an outputter 47 d. The first operational amplifier 47 a has amplifying functions, and has a first slew rate. The first operational amplifier 47 a includes two input terminals and one output terminal. The input terminals are connected to the first inputter 47 b and the second inputter 47 c. The output terminal is connected to the outputter 47 d. The first inputter 47 b and the second inputter 47 c are electrically connected to the resistor 43 a of the detector 43 via the detection path 27. The first inputter 47 b is connected to the first connection terminal 43 d. The second inputter 47 c is connected to the second connection terminal 43 e. The outputter 47 d is electrically connected to the control circuit 23 and the auxiliary interruption controller 45.

The detection path 27 includes a first detection path 27 a and a second detection path 27 b. The first detection path 27 a is connected to the first connection terminal 43 d and the first inputter 47 b of the first current detector 47. The second detection path 27 b is connected to the second connection terminal 43 e and the second inputter 47 c of the first current detector 47. The detection path 27 is configured to electrically connect the first connection terminal 43 d and the second connection terminal 43 e to the first current detector 47. Accordingly, the resistor 43 a and the first current detector 47 are electrically connected with each other.

The first current detector 47 detects a voltage across the resistor 43 a when the drive current Idr is conducted. The first current detector 47 generates a first detection signal Scs. The first detection signal Scs varies in accordance with the detected voltage. The detected voltage varies in accordance with the drive current Idr. Thus, the first detection signal Scs is indicative of the drive current Idr detected by the first current detector 47. In other words, the first current detector 47 detects the magnitude of the drive current Idr based on the voltage across the resistor 43 a. The voltage across the resistor 43 a varies in accordance with a flow of the drive current Idr through the resistor 43 a.

The first current detector 47 generates the first detection signal Scs, and amplifies the first detection signal Scs by the first operational amplifier 47 a. The first current detector 47 outputs the amplified first detection signal Scs from the outputter 47 d. In other words, the first current detector 47 detects current (in other words, the drive current Idr) through the drive current path 25 based on the voltage of the resistor 43 a. The drive current Idr detected by the first current detector 47 is also referred to as the first detection current Idr1 below. The voltage generated across the resistor 43 a corresponds to one example of a first electromagnetic phenomenon of the present disclosure. The magnitude of the drive current Idr (the first detection current Idr1) corresponds to one example of a first detection value of the present disclosure.

In the present embodiment, the first slew rate of the first operational amplifier 47 a and the second slew rate of the second operational amplifier 43 c are equal or substantially equal to each other. Here, “the first slew rate and the second slew rate are substantially equal to each other” means that not only the first slew rate and the second slew rate are exactly the same, but also the first slew rate and the second slew rate have a difference within a permissible range.

The auxiliary interruption controller 45 includes a differential amplifier 45 a, a comparator 45 b, and a reference voltage generator 45 c. The differential amplifier 45 a compares a value of the first detection signal Scs with a value of the second detection signal Smc, and outputs an error signal Sdi corresponding to a difference between the value of the first detection signal Scs and the value of the second detection signal Smc. The first detection signal Scs is a detection signal indicative of the first detection current Idr1, and the second detection signal Smc is a detection signal indicative of the second detection current Idr2. Thus, the error signal Sdi is a signal indicative of a difference between a value of the first detection current Idr1 and a value of the second detection current Idr2.

The reference voltage generator 45 c outputs a reference voltage Vth that is specified in advance. The reference voltage Vth includes a voltage that is set in advance for determining that the first current detector 47 or the second current detector 43 b is in a faulty state. The reference voltage Vth indicates a boundary value between a value of a first error signal Sdi1 and a value of a second error signal Sdi2. The first error signal Sdi1 corresponds to the error signal Sdi when the first current detector 47 or the second current detector 43 b is in the faulty state. The second error signal Sdi2 corresponds to the error signal Sdi when the first current detector 47 and the second current detector 43 b are both in a non-faulty state.

The comparator 45 b compares the error signal Sdi with the reference voltage Vth. If the error signal Sdi is greater than the reference voltage Vth (Sdi>Vth), the comparator 45 b outputs the fault detection signal St2 to place the breaker switch 41 in the interruption state. The comparator 45 b outputs the fault detection signal St2 to the breaker switch 41. The breaker switch 41 is to be placed in the interruption state in response to receipt of the fault detection signal St2, and thus a current conduction via the drive current path 25 is interrupted. This disables conduction of the drive current Idr to the motor driver 21 and the motor 11 from the battery pack 10.

When the breaker switch 41 receives the fault detection signal St2 to be in the interruption state, the interruption state is maintained until the trigger switch 9 is turned off. Specifically, the breaker switch 41 includes a latch circuit 41 a for maintaining the interruption state. The latch circuit 41 a keeps the breaker switch 41 from being in the interruption state until a trigger state signal St3 is received. The trigger state signal St3 indicates that the trigger switch 9 is turned off. The trigger state signal St3 varies in accordance with a potential between a switch 32 and a resistor R1, which will be described below. When the trigger switch 9 is turned on, the trigger state signal St3 has a ground potential equivalent to the ground line 25 b. When the trigger switch 9 is turned off, the trigger state signal St3 has a potential corresponding to the circuit voltage Vcc (i.e. 5V) generated by the regulator 24.

The comparator 45 b compares the error signal Sdi with the reference voltage Vth. If the error signal Sdi is equal or smaller than the reference voltage Vth (Sdi<Vth), the comparator 45 b outputs no fault detection signal St2. In this case, the breaker switch 41 is to be in the established state, permitting current conduction via the drive current path 25. This enables the drive current to be supplied from the battery pack 10 to the motor driver 21 and the motor 11.

That is, the auxiliary interruption controller 45 compares the error signal Sdi with the reference voltage Vth. If the error signal Sdi is greater than the reference voltage Vth, the auxiliary interruption controller 45 controls the breaker switch 41 to be in the interruption state, inhibiting the supply of the drive current Idr to the motor 11. In other words, if the error is greater than the reference voltage Vth, the auxiliary interruption controller 45 placing the breaker switch 41 in the interruption state, thereby interrupting the drive current Idr to the motor 11. The error is a difference in the magnitude between the value of the first detection current Idr1 and the value of the second detection current Idr2. The reference voltage Vth is a threshold for switching the breaker switch 41 to the interruption state. In other words, the reference voltage Vth is the threshold specified in advance.

The controller 20 includes the switch 32 and a light emitting diode 33. The switch 32 is connected to the regulator 24 via the resistor R1, and to a ground 49. Accordingly, the circuit voltage Vcc from the regulator 24 is applied to the switch 32. When the user pulls the trigger switch 9, the switch 32 turns ON. When the user releases the trigger switch 9, the switch 32 turns OFF. The switch 32 is connected to the control circuit 23 via a resistor R2. Thus, the voltage applied to the switch 32 is detected by the control circuit 23.

The light emitting diode 33 has an anode connected to the control circuit 23, and a cathode grounded. The light emitting diode 33 emits a light when an error display signal is input. The error display signal is output from the control circuit 23.

The electric working machine 1 includes a rotation sensor 13. The rotation sensor 13 detects a rotational position and the rotational frequency of the motor 11, and then outputs detection signals Srp indicative of a detection result to the control circuit 23. The “rotational frequency” means the number of revolutions per unit time, and corresponds to a rotational speed.

[1-3. Detector and Circuit Board]

The controller 20 includes a circuit board 26. On the circuit board 26, a portion of the drive current path 25 is arranged. The first current detector 47 and the detector 43 are mounted on the circuit board 26.

FIG. 3 is an enlarged perspective view of a neighboring area of an arrangement region 43 f for the detector 43 (hereinafter, also referred to as a detector arrangement region 43 f) on the circuit board 26. FIG. 3 shows a state where the detector 43 is separated from the circuit board 26. The detector arrangement region 43 f is not limited to a two-dimensional region, but may be a three-dimensional region. The circuit board 26 may include a first surface (not shown) and a second surface (not shown) opposing the first surface. The detector 43 may be disposed on the first surface. The three-dimensional region may extend from the first surface to the second surface.

The drive current path 25 includes a first coupling device 25 a 1 and a second coupling device 25 b 1. The first coupling device 25 a 1 is connected to the first connection terminal 43 d. The second coupling device 25 b 1 is connected to the second connection terminal 43 e. The first coupling device 25 a 1 and the second coupling device 25 b 1 are disposed on the ground line 25 b. The drive current path 25 includes a first partial path 25 b 2. The first partial path 25 b 2 is a portion of the drive current path 25 on the circuit board 26, and the portion is neither the first coupling device 25 a 1 nor the second coupling device 25 b 1. The first partial path 25 b 2 is disposed out of (deviates from) the detector arrangement region 43 f on the circuit board 26. The drive current path 25 is electrically connected to the resistor 43 a in the detector 43, via the first connection terminal 43 d and the second connection terminal 43 e.

The detection path 27 is arranged on the circuit board 26. The detection path 27 includes the first detection path 27 a and the second detection path 27 b. The detection path 27 includes a terminal connection end 27 c and an inclusion region 27 d.

The terminal connection end 27 c includes a first detection end 27 c 1 and a second detection end 27 c 2. The first detection end 27 c 1 is an end of the first detection path 27 a. The first detection end 27 c 1 is electrically connected to the first connection terminal 43 d via the first coupling device 25 a 1. The second detection end 27 c 2 is an end of the second detection path 27 b. The second detection end 27 c 2 is electrically connected to the second connection terminal 43 e via the second coupling device 25 b 1.

The inclusion region 27 d includes a first inclusion region 27 d 1 and a second inclusion region 27 d 2. The first inclusion region 27 d 1 is adjacent to the first detection end 27 c 1 on the first detection path 27 a. The second inclusion region 27 d 2 is adjacent to the second detection end 27 c 2 on the second detection path 27 b. The first inclusion region 27 d 1 on the first detection path 27 a is disposed in the detector arrangement region 43 f on the circuit board 26. The second inclusion region 27 d 2 on the second detection path 27 b is disposed in the detector arrangement region 43 f on the circuit board 26.

The circuit board 26 is a multi-layered board including two or more insulating layers 26 a. The circuit board 26 includes two or more current paths (not shown). An arrangement of the current paths is not limited to an arrangement in which the current paths are disposed on an outmost surface of the circuit board 26, but the current paths may be arranged between the insulating layers 26 a. Such three-dimensional multi-layered arrangement of the current paths enables improvements in a density of current paths on the circuit board 26. In the present embodiment, the current paths include the drive current path 25 and the detection path 27.

The circuit board 26 includes the current paths in at least the detector arrangement region 43 f. The current paths arranged in the detector arrangement region 43 f will be described below.

The current paths are explained with reference to the circuit board 26 including a first current path and a second current path, as schematically shown in FIG. 4. A first current Ia flows through the first current path. A second current Ib flows through second current path. In the detector arrangement region 43 f shown in FIG. 4, the drive current Idr through the resistor 43 a flows in a direction indicated by a hollow arrow Idr.

On a planar surface parallel to a plate surface of the circuit board 26, currents through the circuit board 26 may be resolved into a parallel current component and a perpendicular current component. The parallel current component is directed toward a direction parallel to a current-carrying direction in which currents run in the resistor 43 a. The perpendicular current component is directed toward a direction perpendicular to the current-carrying direction. The parallel current component of the first current Ia (hereinafter, also referred to as a first parallel current component Iax) is indicated by an arrow Tax. Similarly, the parallel current component of the second current Ib (hereinafter, also referred to as a second parallel current component Ibx) is indicated by an arrow Ibx. A vector sum of the first parallel current component Iax and the second parallel current component Ibx corresponds to a resultant parallel current component Icm(=|Ibx−Iax|).

In the circuit board 26 of the present embodiment, the arrangement of the current paths in the detector arrangement region 43 f is adjusted such that the resultant parallel current component Icm is equal to or smaller than 20 mA. In other words, in the electric working machine 1, a total current value of the parallel current components is equal to or smaller than 20 mA.

It is noted that motor drive currents in general electric working machines have a range from 0 to 100 A, and thus current sensors for measuring such motor drive currents have a measurement range of currents from 0 to 100 A. In this case, the measurement range of currents is so broad that a current measurement error may be greater. Further, in a range of low currents (for example, a range from 0 to 20 A) within the measurement range of currents, there are needs for measuring currents with a high accuracy (±0.2 A) to increase a current control accuracy in no-load low speed rotation control (soft no-load) and so forth.

Here, an influence of external currents (or disturbance currents) through the detector arrangement region 43 f on current measurement results provided by the second current detector 43 b is considered. Specifically, the second current detector 43 b that is easily influenced by the external currents is examined. The second current detector 43 b has characteristics, for example, in which a current value of the external currents is equal or substantially equal to a current measurement value measured by the second current detector 43 b at that time. In other words, this current measurement value influenced from the external currents is detected by the second current detector 43 b. If the second current detector 43 b as mentioned above is used, as long as the external currents through the detector arrangement region 43 f are sufficiently small, a current measurement error caused by the influences of the external currents can be kept within a tolerance (±0.2 A). Accordingly, assumed that such sufficiently small values with respect to the current measurement error is defined as “1/10 or smaller of the current measurement error”, a maximum current is limited to 0.02 A (=20 mA) or smaller, which is 1/10 of the tolerance (±0.2 A). The maximum current is allowed to flow through the detector arrangement region 43 f. Thus, the current measurement error caused by the influence of the external currents can be within the tolerance.

Although a case in which two current paths are disposed in the detector arrangement region 43 f is described above, the aforementioned calculation method for calculating the resultant parallel current components is also applied to a case in which three or more current paths are disposed in the detector arrangement region 43 f.

[1-4. Working Machine Control Processing]

Next, a procedure of working machine control processing performed by the CPU 23 a in the control circuit 23 will be described. The working machine control processing is started after the circuit voltage Vcc is supplied to the control circuit 23 and the control circuit 23 is activated.

When the CPU 23 a starts the working machine control processing, an initial setting is firstly performed in S110 (S indicating a step) as shown in FIG. 5. Specifically, the CPU 23 a sets initial values to respective various parameters and respective various flags used in the working machine control processing.

In S120, the CPU 23 a performs a motor stop processing. At the time, the CPU 23 a outputs, to the motor driver 21, the control signals Smd for stopping rotation of the motor 11.

In S130, the CPU 23 a clears a time counter Ct and storage data Dis individually. The time counter Ct and the storage data Dis are internal variables used in calculations performed by the CPU 23 a. The time counter Ct indicates an elapsed time. The storage data Dis indicates time-series data of currents. The time counter Ct is set to an initial value (Ct=0), clearing all the storage data Dis stored in an information storage device.

The information storage device includes a storage medium storing the first detection current Idr1 and the second detection current Idr2. The first detection current Idr1 is the drive current Idr detected by the first current detector 47. The second detection current Idr2 is the drive current Idr detected by the second current detector 43 b. The information storage device stores the storage data Dis that is time-series data of each of the first detection current Idr1 and the second detection current Idr2. The information storage device includes the RAM 23 c, for example.

In S140, the CPU 23 a determines whether the trigger switch 9 is in the ON-state. Upon an affirmative determination, the CPU 23 a proceeds to S150. Upon a negative determination, the CPU 23 a proceeds to S120.

As a result of the affirmative determination in S140, the CPU 23 a proceeds to S150, performing a motor rotation processing. The CPU 23 a outputs, to the motor driver 21, the control signals Smd for rotating the motor 11.

In S160, the CPU 23 a performs a current measurement processing.

The CPU 23 a starts to perform the current measurement processing, firstly adding the time counter Ct in S310, as shown in FIG. 6. In this processing, the time counter Ct is increased by adding 1 (Ct=Ct+1).

In S320, the CPU 23 a determines whether the time counter Ct is equal to or greater than a given cycle determination value Cth. Upon an affirmative determination, the CPU 23 a proceeds to S330, and upon a negative determination, the CPU 23 a proceeds to S340. In the cycle determination value Cth, a value corresponding to a memory cycle Tm is set. The memory cycle Tm is set in accordance with a period of storing data used in a failure diagnosis of the first current detector 47 and the second current detector 43 b. The memory cycle Tm is, for example, set at 10 [msec]. The data used in the failure diagnosis are detection values of the first current detector 47 and the second current detector 43 b, in particular, the first detection current Idr1 and the second detection current Idr2.

Upon the affirmative determination in S320, the CPU 23 a proceeds to S330, clearing the time counter Ct. Accordingly, the time counter Ct is set to the initial value (Ct=0).

The CPU 23 a proceeds to S340, acquiring the first detection current Idr1 detected by the first current detector 47, and the second detection current Idr2 detected by the second current detector 43 b. At the time, the CPU 23 a acquires the value of the first detection current Idr1 by receipt of the first detection signal Scs from the first current detector 47. The CPU 23 a acquires the value of the second detection current Idr2 by receipt of the second detection signal Smc from the second current detector 43 b.

The CPU 23 a proceeds to S350, storing the first detection current Idr1 and the second detection current Idr2 in the information storage device. The CPU 23 a stores the first detection current Idr1 and the second detection current Idr2 in a memory region to be instructed by the time counter Ct.

After completion of the current measurement processing in S350, the CPU 23 a returns to the working machine control processing. Subsequently, the CPU 23 a performs a failure diagnosis processing in S170. In S170, the CPU 23 a makes a diagnosis on whether the first current detector 47 or the second current detector 43 b is in a failure.

The CPU 23 a starts the failure diagnosis processing, firstly extracting a maximum value and a minimum value of the first detection current Idr1 that have been detected by the first current detector 47 in S410, as shown in FIG. 7. At the time, the CPU 23 a extracts the maximum value and the minimum value of the first detection current Idr1 in the storage data Dis concerning the first detection current Idr1.

In S420, the CPU 23 a extracts a maximum value and a minimum value of the second detection current Idr2 that have been detected by the second current detector 43 b. At the time, the CPU 23 a extracts the maximum value and the minimum value of the second detection current Idr2 in the storage data Dis concerning the second detection current Idr2.

In S430, the CPU 23 a determines whether a fluctuation value ΔIdr of the second detection current Idr2 is equal to or smaller than a fluctuation determination value Ith that is specified in advance (ΔIdr≤Ith). Upon an affirmative determination, the CPU 23 a proceeds to S440. Upon a negative determination, the failure diagnosis processing is terminated. The fluctuation value ΔIdr is a difference between the maximum value and the minimum value of the second detection current Idr2. The magnitude of the fluctuation determination value Ith is to be set such that when the drive current Idr actually flowing through the drive current path 25 is in a stable state, the affirmative determination is to be made in S430.

At this time, the CPU 23 a firstly calculates the fluctuation value ΔIdr that is the difference between the maximum value and the minimum value of the second detection current Idr2 during the memory cycle Tm. Subsequently, the CPU 23 a compares the fluctuation value ΔIdr with the fluctuation determination value Ith to determine whether the fluctuation value ΔIdr is smaller than the fluctuation determination value Ith.

For example, in a current waveform shown in FIG. 8, values of the fluctuation value ΔIdr in three diagnosis periods Tt1, Tt2, and Tt3 corresponding to the memory cycles Tm are fluctuation values ΔI1, ΔI2, and ΔI3, respectively. The fluctuation values ΔI1 and ΔI3 are smaller than the fluctuation determination value Ith; however, the fluctuation value ΔI2 is greater than the fluctuation determination value Ith. Accordingly, determinations in the diagnosis periods Tt1 and Tt3 are affirmative in S430, and then a comparison process is performed in S460, which will be described below. On the other hand, a determination in the diagnosis period Tt2 is negative in S430, and then the comparison process is not performed in S460.

Returning to FIG. 7, upon the affirmative determination in S430, the CPU 23 a calculates, in S440, a first mean value I1 avg based on the storage data Dis of the first detection current Idr1. The first mean value I1 avg indicates a mean value of the first detection current Idr1. At the time, the CPU 23 a calculates the first mean value I1 avg using all values of the first detection current Idr1 in a diagnosis period Tt.

In S450, the CPU 23 a calculates a second mean value I2 avg that is a mean value of the second detection current Idr2 based on the storage data Dis of the second detection current Idr2. The second mean value I2 avg indicates a mean value of the second detection current Idr2. At the time, the CPU 23 a calculates the second mean value I2 avg using all values of the second detection currents Idr2 in the diagnosis period Tt.

In S460, the CPU 23 a determines whether an absolute value of a difference between the first mean value I1 avg and the second mean value I2 avg (=|I1 avg-I2 avg|) is greater than a fault determination value Ath that is specified in advance. Upon an affirmative determination, the CPU 23 a proceeds to S470. Upon a negative determination, the CPU 23 a terminates the failure diagnosis processing. The fault determination value Ath is set to a numerical value such that the determination in S460 is affirmative when the first current detector 47 and/or the second current detector 43 b are/is in a faulty state or a failure state. In other words, the fault determination value Ath is set so as to correspond to the absolute value of the difference when the first current detector 47 and/or the second current detector 43 b are/is in the faulty state or the failure state.

Upon the affirmative determination in S460, the CPU 23 a sets a sensor fault flag Fs in S470. The sensor fault flag Fs indicates that the first current detector 47 or the second current detector 43 b is in the faulty state.

In other words, the CPU 23 a performs the failure diagnosis processing to make a faulty state determination whether the first current detector 47 or the second current detector 43 b is in the faulty state, based on a comparison result of the first detection current Idr1 and the second detection current Idr2.

After completing the failure diagnosis processing, the CPU 23 a returns to the working machine control processing, and in S180 determines whether the current sensor is faulty. Upon an affirmative determination in S180, the CPU 23 a proceeds to S190. Upon a negative determination in S180, the CPU 23 a proceeds to S140. At the time, the CPU 23 a determines whether the current sensor is faulty based on whether the sensor fault flag Fs is in a setting state.

Upon the affirmative determination in S180, the CPU 23 a performs the motor stop processing in S190. At the time, the CPU 23 a outputs not only the control signals Smd to the motor driver 21 so as to stop rotation of the motor 11, but also the command signal St1 to the breaker switch 41 so as to control the breaker switch 41 to be in the interruption state.

In other words, the CPU 23 a is configured to inhibit the supply of the drive current Idr to the motor 11 by stopping to the drive current Idr to the motor 11 via the motor driver 21, as well as by controlling the breaker switch 41 to be in the interruption state.

In S200, the CPU 23 a performs an error display processing. At the time, the CPU 23 a outputs an error display signal to the light emitting diode 33, emitting the light emitting diode 33. This enables the user to be notified that either the first current detector 47 or the second current detector 43 b is in the faulty state.

[1-5. Effects]

The electric working machine 1 includes the first current detector 47 and the second current detector 43 b, thereby enabling each of the first detection current Idr1 and the second detection current Idr2 to be detected based on the first electromagnetic phenomenon and the second electromagnetic phenomenon. The first electromagnetic phenomenon and the second electromagnetic phenomenon vary in accordance with the flow of the drive current Idr through the resistor 43 a. The first electromagnetic phenomenon is the voltage across the resistor 43 a, and the second electromagnetic phenomenon is the magnetic field around the resistor 43 a.

Thus, if both the first current detector 47 and the second current detector 43 b are in the non-faulty state, the first detection current Idr1 and the second detection current Idr2 are equivalent to each other in magnitude. On the other hand, if the first current detector 47 and/or the second current detector 43 b is/are faulty, the first detection current Idr1 and the second detection current Idr2 are different from each other in magnitude.

Accordingly, the CPU 23 a performs the failure diagnosis processing to make a fault determination based on the comparison result of the first detection current Idr1 and the second detection current Idr2. This enables the electric working machine 1 to determine a fault in the first current detector 47 or the second current detector 43 b.

As a result, the electric working machine 1 can avoid continuously detecting the drive current Idr with the first current detector 47 in the faulty state or the second current detector 43 b in the faulty state. This enables the electric working machine 1 to avoid driving the motor 11 with the drive current Idr that is not appropriate, reducing a failure in the electric working machine 1.

Further, the electric working machine 1 includes the breaker switch 41 and the control circuit 23 (in particular, the CPU 23 a) that outputs the command signal St1. The electric working machine 1 stops the supply of the drive current to the motor 11 when the first current detector 47 or the second current detector 43 b is in the faulty state. Accordingly, the electric working machine 1 avoids a runaway of the motor 11 caused by the fault in the first current detector 47 or the second current detector 43 b, enabling reduction in damages of the motor 11 and the electric working machine 1.

Furthermore, the electric working machine 1 includes the auxiliary interruption controller 45 that outputs the command signal St1 and that is different from the control circuit 23. When the error between the first detection current Idr1 and the second detection current Idr2 is greater than a determination criteria defined as the reference voltage Vth, the auxiliary interruption controller 45 switches the breaker switch 41 to the interruption state, interrupting the drive current Idr to the motor 11.

In the electric working machine 1, in a case in which the control circuit 23 is unable to switch the breaker switch 41 to the interruption state due to some cause, the auxiliary interruption controller 45 places the breaker switch 41 in the interruption state. This enables the motor current path 25 to be interrupted. Accordingly, in a case in which the first current detector 47 or the second current detector 43 b is in the faulty state, the electric working machine 1 stops the supply of the drive current to the motor 11.

In the electric working machine 1, the first slew rate and the second slew rate are equal or substantially equal to each other. In this case, it is less likely to cause a delay in change between the first detection signal Scs amplified by the first current detector 47 and the second detection signal Smc amplified by the second operational amplifier 43 c.

Thus, when the electric working machine 1 compares the first detection current Idr1 with the second detection current Idr2, it can be reduced that an error caused by a delay in change between the first detection signal Scs and the second detection signal Smc occurs.

Further, the electric working machine 1 includes the detector 43, the circuit board 26, and the detection path 27. The first inclusion region 27 d 1 is arranged in the detector arrangement region 43 f. The second inclusion region 27 d 2 is arranged in the detector arrangement region 43 f. The first partial path 25 b 2 of the motor current path 25 is disposed out of (or deviates from) the detector arrangement region 43 f.

In the electric working machine 1, the inclusion region 27 d and the first partial path 25 b 2 are arranged in areas different (or distinct) from each other on the circuit board 26. Thus, the electric working machine 1 enables reduction in an electromagnetic interference of the detection path 27 (in particular, the inclusion region 27 d) with the motor current path 25 (in particular, the first partial path 25 b 2) in a surrounding area of the first connection terminal 43 d and a surrounding area of the second connection terminal 43 e.

Further, in the electric working machine 1, the circuit board 26 includes the current paths in the detector arrangement region 43 f. As explained with reference to FIG. 4, with respect to the current flowing through the current paths in the detector arrangement region 43 f, the total current value Icm of the first parallel current component lax and the second parallel current component Ibx is equal to or smaller than 20 mA. The electric working machine 1 as configured above enables reduction in influence of the first parallel current component Iax and the second parallel current component Ibx on the second current detector 43 b. This enables reduction in a detection error when the drive current Idr of the current path 25 (in particular, the second detection current Idr2) is detected based on the magnetic fields around the resistor 43 a.

Furthermore, in the electric working machine 1, the CPU 23 a performs S430 to calculate the fluctuation value ΔIdr. In S430, the CPU 23 a determines whether the fluctuation value ΔIdr is greater than the fluctuation determination value Ith that is specified in advance.

In response to the determination that the fluctuation value ΔIdr is equal to or smaller than the fluctuation determination value Ith (in other words, the affirmative determination in S430), the CPU 23 a performs S460 to make the faulty state determination based on the first detection current Idr1 and the second detection current Idr2 in the diagnosis period Tt as a determination period.

On the contrary, in response to the determination that the fluctuation value ΔIdr is greater than the fluctuation determination value Ith (in other words, the negative determination in S430), the CPU 23 a does not perform S460. That is, the CPU 23 a makes no faulty state determination based on the first detection current Idr1 and the second detection current Idr2 in the diagnosis period Tt.

In the electric working machine 1 as configured above, in response to a determination result, which is determined by the CPU 23 a in S430, the CPU 23 a determines whether to perform S460, in other words, the electric working machine 1 determines whether to make the faulty state determination. In the determination period in which the fluctuation value ΔIdr is determined to be greater than the fluctuation determination value Ith, the current through the drive current path 25 is widely fluctuated and may cause an erroneous determination in the faulty state determination. Thus, the electric working machine 1 causes the CPU 23 a to make no faulty state determination (S460) during the determination period in which the fluctuation value ΔIdr is determined to be greater than the fluctuation determination value Ith. This enables reduction in the erroneous determination in the faulty state determination.

Further, in the electric working machine 1, to compare the first detection current Idr1 with the second detection current Idr2 in S460, the CPU 23 a compares the first mean value I1 avg as the mean value of the first detection current Idr1, with the second mean value I2 avg as the mean value of the second detection current Idr2. As described above, the first mean value I1 avg and the second mean value I2 avg are used for the first detection current Idr1 and the second detection current Idr2, respectively. This enables reduction in an influence of a momentary noise with respect to the first detection current Idr1 and the second detection current Idr2, while making the faulty state determination. Accordingly, the electric working machine 1 enables reduction in the influence of the momentary noise while making the faulty state determination. Thus, a decrease in determination accuracy of the fault determination can be avoided.

[1-6. Correspondence Between Terms]

The resistor 43 a corresponds to one example of the resistor of the present disclosure. The CPU 23 a performing S460 corresponds to one example of the fault determiner of the present disclosure. The CPU 23 a performing S190 corresponds to one example of the first interruption controller of the present disclosure. The auxiliary interruption controller 45 corresponds to one example of the second interruption controller of the present disclosure. The breaker switch 41 corresponds to one example of the switch of the present disclosure.

2. Other Embodiments

Embodiments of the present disclosure have been described hereinabove. Nevertheless, the present disclosure is not limited to the aforementioned embodiments. The present disclosure can be embodied in various forms without departing from the spirit of the present disclosure.

(2a) In the aforementioned embodiment, a form of the information storage device including the RAM 23 c is described, but the information storage device is not limited to such form. In other words, the information storage device may be any kinds of storage media capable of storing time-series data of each of the first detection current and the second detection current. For example, the information storage device may include a storage medium such as an external memory or an external HDD connected to the control circuit 23.

(2b) In the aforementioned embodiment, the CPU 23 a compares the first mean value I1 avg with the second mean value I2 avg in S460. However, S460 is not limited to this processing. For example, in S460, the CPU 23 a may use a momentary value of the first detection current Idr1 and a momentary value of the second detection current Idr2, instead of the first mean value I1 avg and the second mean value I2 avg, to calculate an absolute value of a difference between the momentary values of them, and compare the calculated absolute value of the difference with the fault determination value Ath. In this case, the CPU 23 a may obtain the momentary values of the first detection current Idr1 and the second detection current Idr2, instead of the first mean value I1 avg and the second mean value I2 avg, in S440 and S450. Such configuration enables an increase in processing load in the CPU 23 a associated with the mean value calculations in S440 and 5450.

It is noted that the processing in S460 is only required to determine whether there is a great difference between the first detection current Idr1 and the second detection current Idr2.

(2c) In the aforementioned embodiment, the fluctuation value ΔIdr is calculated using the second detection current Idr2, but a mode of calculating the fluctuation value ΔIdr is not limited to such mode. For example, the CPU 23 a may use the maximum value and minimum value of the first detection current Idr1 to calculate the fluctuation value ΔIdr when performing S430. Use of the first detection current Idr1 or the second detection current Idr2 enables a determination of a changing state of the drive current Idr, thereby reducing the erroneous determination in the faulty state determination.

(2d) In the aforementioned embodiment, the CPU 23 a uses all the first detection current Idr1 and the second detection current Idr2 in the diagnosis period Tt when calculating the first mean value I1 avg and the second mean value I2 avg (S440, S450). However, a mode of calculating the first detection current Idr1 and the second detection current Idr2 is not limited to such mode. For example, the number of data (or samples) used for calculating the first mean value I1 avg and the second mean value I2 avg may be reduced. Such calculation enables reduction in processing load in the CPU 23 a associated with the mean value calculations in S440 and S450.

(2e) Two or more functions achieved by a single element in the aforementioned embodiments may be achieved by elements, or a function achieved by elements may be achieved by a single element. In addition, at least portion of a configuration in one of the aforementioned embodiments may be substituted by a well-known configuration having the similar functions. In addition, portion of the configuration of each embodiment above may be omitted. Moreover, at least portion of an element in one of the aforementioned embodiments may be added to, or may be replaced by, another one of the aforementioned embodiments. Any modes within the scope of the technical ideas identified from the claim language are embodiments of the present disclosure. 

What is claimed is:
 1. An electric working machine comprising: a motor; a drive current path configured to supply a drive current to the motor, the drive current being supplied to the motor to drive the motor; a resistor disposed on the drive current path so as to detect a magnitude of the drive current; a first current detector configured to generate a first detection signal based on a voltage across the resistor, the first detection signal indicating the magnitude of the drive current; a second current detector configured to generate a second detection signal based on a magnetic field around the resistor, the second detection signal indicating the magnitude of the drive current; a switch disposed on the drive current path, the switch being configured to be switched between an established state and an interruption state, the switch in the established state being configured to establish the drive current path, and the switch in the interruption state being configured to interrupt the drive current path; a control circuit configured to perform a working machine control processing, the working machine control processing including: repeatedly acquiring the first detection signal to thereby acquire a first series of detection values; calculating a first mean value, the first mean value indicating a mean of the first series of detection values; repeatedly acquiring the second detection signal to thereby acquire a second series of detection values; calculating a second mean value, the second mean value indicating a mean of the second series of detection values; determining whether the first current detector or the second current detector is in the faulty state based on the first mean value and the second mean value is in the faulty state; and placing the switch in the interruption state in response to determining that the first current detector or the second current detector is in the faulty state; and an auxiliary interruption controller disposed separately from the control circuit, the auxiliary interruption controller being configured to place the switch in the interruption state in accordance with an error being greater than a determination criteria, the error corresponding to a difference between the first detection signal and the second detection signal, the determination criteria corresponding to a threshold to place the switch in the interruption state.
 2. An electric working machine comprising: a motor; a drive current path configured to supply a drive current to the motor, the drive current being supplied to the motor to drive the motor; a resistor disposed on the drive current path so as to receive the drive current; a first current detector configured to detect a first detection value based on a first electromagnetic phenomenon with respect to the resistor, the first detection value indicating a magnitude of the drive current, the first electromagnetic phenomenon varying in accordance with a flow of the drive current through the resistor; a second current detector configured to detect a second detection value based on a second electromagnetic phenomenon with respect to the resistor, the second detection value indicating the magnitude of the drive current, the second electromagnetic phenomenon varying in accordance with the flow of the drive current through the resistor, the second electromagnetic phenomenon being different from the first electromagnetic phenomenon; and a fault determiner configured to perform a faulty state determination based on the first detection value and the second detection value, and to determine whether the first current detector or the second current detector is in a faulty state during the faulty state determination.
 3. The electric working machine according to claim 2, wherein the first electromagnetic phenomenon corresponds to a voltage across the resistor; and wherein the second electromagnetic phenomenon corresponds to a magnetic field around the resistor.
 4. The electric working machine according to claim 2, further comprising: a switch disposed on the drive current path, the switch being configured to switch between an established state and an interruption state, the switch in the established state being configured to establish the drive current path, and the switch in the interruption state being configured to interrupt the drive current path; and a first interruption controller configured to place the switch in the interruption state in response to an establishment of a first determination condition, the first determination condition being established in response to the fault determiner determining that the first current detector or the second current detector is in the faulty state.
 5. The electric working machine according to claim 4, further comprising a second interruption controller provided independently from the first interruption controller, wherein the second interruption controller is configured to place the switch in the interruption state in accordance with an error being greater than a determination criteria, the error corresponding to a difference between the first detection value and the second detection value, the determination criteria corresponding to a threshold to place the switch in the interruption state.
 6. The electric working machine according to claim 2, wherein the first current detector is configured to outputs a first detection signal, the first detection signal varying in accordance with the first detection value, wherein the second current detector is configured to output a second detection signal, the second detection signal varying in accordance with the second detection value, and wherein the electric working machine including, a first operational amplifier having a first slew rate, the first operational amplifier being configured to amplify the first detection signal; and a second operational amplifier having a second slew rate, the second operational amplifier being configured to amplify the second detection signal, and the first slew rate being equal or substantially equal to the second slew rate.
 7. The electric working machine according to claim 2, further comprising: a detector including the resistor, the second current detector, a first connection terminal, and a second connection terminal, the resistor having a first end and a second end, the first connection terminal being electrically connected to the first end, and the second connection terminal being electrically connected to the second end; a circuit board including the drive current path, the first current detector, and the detector thereon; and a detection path disposed on the circuit board, the detection path electrically connecting the resistor to the first current detector.
 8. The electric working machine according to claim 7, wherein the drive current path is electrically connected to the resistor via the first connection terminal and the second connection terminal, wherein the circuit board including a first area where the detector is disposed, wherein the drive current path include a first partial path disposed out of the first area on the circuit board, and wherein the drive current path is connected to the first connection terminal and the second connection terminal in the first area, the detection path including: a detection end connected to the first connection terminal and the second connection terminal, and an inclusion region adjacent to the detection end, the inclusion region being included in the first area.
 9. The electric working machine according to claim 8, wherein the circuit board includes two or more current paths in the first area, wherein the two or more current paths are configured to flow a circuit board current, wherein the circuit board current includes a current component parallel to the flow of the drive current through the resistor, and wherein the current component in the first area has a magnitude equal to or less than 20 mA.
 10. The electric working machine according to claim 2, further comprising a current fluctuation determiner configured to determine whether a fluctuation value is greater than a fluctuation determination value, the fluctuation value corresponding to a first error or a second error in a determination period, the determination period being specified in advance to determine the fluctuation value, the first error being a difference between a maximum value of the first detection value and a minimum value of the first detection value, the second error being a difference between a maximum value of the second detection value and a minimum value of the second detection value, and the fluctuation determination value corresponding to the fluctuation value in response to the first current detector or the second current detector in the faulty state, wherein the fault determiner is configured to perform the faulty state determination based on the first detection value and the second detection value during the determination period, in response to the current fluctuation determiner determining that the fluctuation value is equal to or less than the fluctuation determination value.
 11. The electric working machine according to claim 2, wherein the fault determiner is configured to repeatedly acquire the first detection value to thereby acquire a first series of detection values, wherein the fault determiner is configured to calculate a first mean value, the first mean value indicating a mean of the first series of detection values, wherein the fault determiner is configured to repeatedly acquire the second detection value to thereby acquire a second series of detection values, wherein the fault determiner is configured to calculate a second mean value, the second mean value indicating a mean of the second series of detection values, and wherein the fault determiner is configured to perform the faulty state determination based on the first mean value and the second mean value.
 12. The electric working machine according to claim 2, further comprising a battery pack configured to output the drive current.
 13. The electric working machine according to claim 2, further comprising a trigger switch configured to be pulled by a user of the electric working machine, the trigger switch being turned on in response to the user pulling the trigger switch, wherein the fault determiner is configured to determine that the first current detector and the second current detector are in a non-faulty state, in response to (i) the first current detector or the second current detector is in the faulty state, and (ii) the trigger switch being turned off.
 14. The electric working machine according to claim 2, wherein the resistor is disposed on the drive current path so as to detect the magnitude of the drive current.
 15. A method of detecting a fault in an electric working machine, the method comprising: detecting a first detection value by a first current detector of the electric working machine based on a first electromagnetic phenomenon with respect to a resistor of the electric working machine, the drive current being supplied to a motor of the electric working machine to drive the motor, the resistor being disposed in the electric working machine so as to receive the drive current, and the first electromagnetic phenomenon varying depending on a flow of the drive current through the resistor; detecting a second detection value by a second current detector of the electric working machine based on a second electromagnetic phenomenon with respect to the resistor, the second electromagnetic phenomenon being different from the first electromagnetic phenomenon, and the second electromagnetic phenomenon varying depending on the flow of the drive current through the resistor; and detecting occurrence of a fault in the first current detector or the second current detector based on the first detection value and the second detection value. 